Search results for "Free-radical"

Horseradish peroxidase-catalyzed oxidation of chlorophyll a with hydrogen peroxide Characterization of the products and mechanism of the reaction

AbstractHorseradish peroxidase was verified to catalyze, without any phenol, the hydrogen peroxide oxidation of chlorophyll a (Chl a), solubilized with Triton X-100. The 132(S) and 132(R) diastereomers of 132-hydroxyChl a were characterized as major oxidation products (ca. 60%) by TLC on sucrose, UV–vis, 1H, and 13C NMR spectra, as well as fast-atom bombardment MS. A minor amount of the 152-methyl, 173-phytyl ester of Mg-unstable chlorin was identified on the basis of its UV–vis spectrum and reactivity with diazomethane, which converted it to the 131,152-dimethyl, 173-phytyl ester of Mg-purpurin 7. The side products (ca. 10%) were suggested to include the 173-phytyl ester of Mg-purpurin 18,…

Measurement of white wines resistance against oxidation by Electron Paramagnetic Resonance spectroscopy

2018

International audience; Free radical theory of aging hypothesizes that oxygen-derived radicals are responsible for the storage-related flavor instability in wine. In an optimal situation, a balanced-distribution exists between oxidants and antioxidants among wines intrinsic/extrinsic metabolites. Based on the kinetic study of POBN-1-hydroxyethyl spin adduct (POBN-1-HER) formation in wines initiated via the Fenton reaction, a novel tool based on EPR spin trapping methodology was developed to quantify wines resistance against oxidation. Antioxidant capacities of wines were evaluated according to POBN-1-HER maximum signal intensity (Imax POBN-1-HER) and rate formation (r(POBN-1-HER)) kinetic p…

Ultrasound-assisted MnO2 catalyzed homolysis of peracetic acid for phenol degradation: The assessment of process chemistry and kinetics

2013

Abstract The combination of peracetic acid (PAA) and heterogeneous catalyst (MnO 2 ) was used for the degradation of phenol in an aqueous solution in the presence of ultrasound irradiation (US). As a relevant source of free radicals (e.g. OH), peracetic acid was comprehensively studied by means of electron spin resonance (ESR) spin trapping (ST) techniques with the subsequent identification of free radicals by simulation based fitting (SBF) technique. The radical reaction mechanism, where hydroxyl radical was a primary product of O O bond rupture of PAA, was established taking into account radical reactions, occurring during sonolysis. The potential barriers and the reaction heat were deter…

Cell cycle: Aetiology of age-associated aneuploidy: a mechanism based on the 'free radical theory of ageing'

1995

A general model is put forward to explain the mechanism by which age-associated aneuploidies are produced. This is based on the free radical theory of ageing, which assumes a rise in oxidative stress with age. It is proposed that determination of indicators of oxidative stress in oocytes from various sources could be a first step in the testing of this hypothesis.

The Free Radical Theory of Aging Revisited: The Cell Signaling Disruption Theory of Aging

2013

AbstractSignificance: The free radical theory of aging has provided a theoretical framework for an enormous amount of work leading to significant advances in our understanding of aging. Up to the turn of the century, the theory received abundant support from observations coming from fields as far apart as comparative physiology or molecular biology. Recent Advances: Work from many laboratories supports the theory, for instance showing that overexpression of antioxidant enzymes results in increases in life-span. But other labs have shown that in some cases, there is an increased oxidative stress and increased longevity. The discovery that free radicals can not only cause molecular damage to …

Mitochondria and Ageing

2018

Mitochondria are the major sites of oxygen utilisation for energy production in cells. Indeed, all the reactions of the Krebs’ Cycle take place in mitochondria and they produce NADH and succinate, which are then oxidised in the respiratory chain. Experiments dating back to the early part of the twentieth century seemed to indicate that at a high rate of oxygen consumption (referred to gram of body weight) was normally associated with a low maximum lifespan. Thus, it was thought that it was the rate of oxygen utilisation that was related to “the rate of living”. However, more recent data pointed out that birds are unique because they combine high rates of oxygen consumption with a high maxim…

Kinetic treatment of slow initiation in living carbocationic polymerization and investigation of benzyl halides as initiators for the polymerization …

1998

In contrast to earlier conclusions it is demonstrated that kinetic analysis of incremental monomer addition (IMA) experiments for living carbocationic polymerizations with slow initiation leads only to the ratio of apparent rate constants of initiation and propagation. The apparent rate constants depend on the true (bimolecular) rate constants and on the positions of the equilibria between dormant and active states of initiator and polymer chain ends, respectively. The same considerations are true for other living processes involving dormant species, e.g., group transfer polymerization or controlled radical polymerization. Slow initiation of living carbocationic polymerization of isobutylen…

Primary radical termination and chain transfer in vinyl polymerization

1974

Cyclodextrins in polymer synthesis: free radical polymerization of cyclodextrin host-guest complexes of methyl methacrylate or styrene from homogenou…

2000

The polymerization of methylated β-cyclodextrin (m-β-CD) 1 : 1 host-guest compounds of methyl methacrylate (MMA) (1) or styrene (2) is described. The polymerization of complexes 1 a and 2 a was carried out in water with potassium peroxodisulfate (K2S2O8)/sodium hydrogensulfite (NaHSO3) as radical redox initiator at 60°C. Unthreading of m-β-CD during the polymerization led to water-insoluble poly(methyl methacrylate) (PMMA) (3) and polystyrene (4). By comparison, analogously prepared polymers from uncomplexed monomers 1 and 2 in ethanol as organic solvent with 2,2′-azoisobutyronitrile (AIBN) as radical initiator showed significantly lower molecular weights and were obtained in lower yields i…

Mitochondrial glutathione oxidation correlates with age-associated oxidative damage to mitochondrial DNA

1996

Mitochondria may be primary targets of free radical damage associated with aging. We have found that mitochondrial glutathione is markedly oxidized with aging in rats and mice. The oxidized to reduced glutathione ratio rises with aging in the liver, kidney, and brain. The magnitude of these changes is much higher than that previously found in whole cells of any species previously studied. In the liver, this ratio (expressing GSSG as a percent of GSH) changed from 0.77 +/- 0.19% (n=5) in young rats to 2.47 +/- 1.25% (n=5) in old ones, i.e., 320% of the controls. In the brain and kidney, values for old rats were, respectively, 600 and 540% higher than those of young rats. A marked oxidation o…